When taking the subway during rush hour, here are some stuff to keep in mind:

The portion of the yellow subway line (Yonge-University-Spadina line) running on Yonge Street (from Finch to Union, and especially south of Bloor-Yonge) can get REALLY busy during the rush hour. You may want to use the part of the line running on University and Spadina Avenues (from Downsview to Union) as it is a little less busy.

TRY TO AVOID GETTING OFF AT BLOOR-YONGE STATION DURING RUSH HOUR. It is the busiest station in the whole TTC system (and the busiest rapid transit station in North America!) and is extraordinarily crowded during rush hour - they even have to use crowd control measures there! If you're on the green line (Bloor-Danforth) and wish to go downtown, change trains at St. George station - while it is still quite crowded it is less busy than Bloor-Yonge station.

If you are heading to the Financial District try to use St. Andrew station during rush hour. Although all three stations serving the Financial District are among the busier stations in the TTC system, St. Andrew is slightly less busy than King. Try to avoid Union altogether during the rush hour as it is extremely busy.